The present invention is in the field of electronic cooling and temperature regulation.
This invention relates to heat sink apparatus useful in electronic devices. More specifically, this invention relates to the removal of heat from microelectronics that are useful in computerized devices
The problem of heat removal has become an important factor in the advancement of microelectronics, due to drastically increased integration density of chips in digital devices as well as an increased current-voltage handling capability of power electronic devices. The task of removing a large amount of dispersed heat from a constrained, small space is often beyond the capability of conventional cooling techniques. New methods with heat removal capabilities at least one order larger than that of conventional ones are therefore required.
Although described with respect to the fields of computers and microelectronics, it will be appreciated that similar advantages of a high performance and compact cooling scheme may be realized in other applications of the present invention. Such advantages may become apparent to one of ordinary skill in the art in light of the present disclosure or through practice of the invention.
The present invention includes heat sinks, heat sink devices, and heat sink systems. The present invention may also be used as a heat source, a heat source device, and in heat source systems, in accordance with methods of heat transfer known to one skilled in the art. The invention also includes machines or electronic devices using these aspects of the invention. The present invention may also be used to upgrade, repair or retrofit existing machines or electronic devices or instruments of these types, using methods and components known in the art.
The present invention is based on a multi-layer micro-channel heat sink design. Micro-channel heat sink has been studied and tested as a high performance and compact cooling scheme in microelectronics cooling applications. It is shown that the thermal resistance as low as 0.03xc2x0 C./W is obtainable for micro-channel heat sinks, which is substantially lower than conventional channel-sized heat sinks. Design factors that have been studied include coolant selection (air and liquid coolant), inclusion of phase change (one phase and two phase), and structural optimization.
One drawback of micro-channel heat sink is the relatively higher temperature rise along the micro-channels compared to that for the traditional heat sink designs. In the micro-channel heat sink the large amount of heat generated by semiconductor chips is carried out from the package by a relatively small amount of coolant, the coolant thereby exiting at a relatively high temperature.
This undesirable temperature gradient is an important consideration in the design of an electronic cooling scheme. A large temperature rise produces thermal stresses in chips and packages due to the coefficient of thermal expansion (CTE) mismatch among different materials thus undermining device reliability. Furthermore, a large temperature gradient is undesirable for the electrical performance since many electrical parameters are adversely affected by a substantial temperature rise. For instance, in power electronic devices electrical-thermal instability and thermal breakdown could occur within a high temperature region.
In one-layered micro-channel heat sink design, increasing the pressure drop across the channels can control bulk temperature rise along the channels. A larger pressure drop forces coolant to move faster through the channel. This requires a more powerful pumping power supply, generating more noise, and requiring bulkier packaging. Multi-phase micro-channel heat sink is an alternative method for eliminating the temperature variations, in which the utilization of latent heat can achieve a uniform temperature profile on the heating surface. However, a multi-phase scheme can have several drawbacks, such as a complicated structure and a much larger pressure drop required for the gas-liquid mixture to flow inside the minute conduits.
The present invention reduces the undesired temperature variation in the streamwise direction for the micro-channel heat sink by a design improvement, instead of increasing the pressure drop. The design in the present invention is based upon stacking multiple layers of micro-channel heat sink structures, one atop the other, with coolant flowing in different directions in each of the adjacent micro-channel layers. For such an arrangement, streamwise temperature rise for the coolant and the substrate in each layer may be compensated through conduction between the layers, resulting in a substantially reduced temperature gradient. The flow loop can be similar to the one designed for the one-layered micro-channel heat sink, except that the flow loop should branch to allow the coolant to flow from different directions, or the same direction, into each of the layers.
In the present invention, the thermal performance of the proposed multi-layered micro-channel heat sink is examined numerically using a finite element method. Optimization issues for design parameters are addressed as well. Although a one-layered micro-channel heat sink has been extensively studied, the proposed multi-layered structure concept has never been reported.
The present invention includes a multi-layered micro-channeled heat sink for use with a heat-generating surface. The heat sink has at least one first layer having a plurality of micro-channels. One of these first layers is in thermal contact with the heat-generating surface. The heat sink also has at least one second layer comprising a plurality of micro-channels. Each second layer is in thermal contact with at least one first layer. Preferably, the layers alternate between first and second layers. The heat sink also comprises a device for circulating a coolant through these layers. The coolant preferably flows through each first layer in a common direction and through each second layer in a direction opposite that common direction.
Also included in the present invention is a multi-layered micro-channeled heat sink for use in conjunction with heat-generating surface. The heat sink contains multiple layers, each layer comprised of several micro-channels. Each layer is in thermal contact with at least one other layer. One of the layers is also in thermal contact with the heat-generating surface. The heat sink includes a device for circulating a coolant or other heat-transferable fluid through these layers, such that coolant flows through at least two of the layers in different directions. Preferably, coolant flows through each adjacent layer in a different direction.
The present invention also includes an electronic device with multi-layered micro-channeled heat sink. The device includes electronic circuitry capable of generating heat. The device contains a plurality of layers, each layer comprised of a plurality of micro-channels. Each layer is in thermal contact with at least one other layer, and one of the layers is also in thermal contact with the electronic circuitry. The electronic device also includes a device for circulating a coolant through the layers, such that the coolant flows through at least two of the layers in different directions.
The heat sink or electronic device may be made of any appropriate material consistent with its intended function as reflected in the present disclosure. For instance, the channel walls may be made of silicon. The systems can be augmented by the addition of any related device, including a cooling or heating device, a heat exchange device, a coolant or heating fluid filter, a coolant or heating fluid reservoir, and/or a flow-generating device. Typically, the dimensions of the individual micro-channels should be less than one-sixteenth of an inch in height and width, and comparable to the size of the heat generating or heat absorbing substrate in length. EDM is an example of a technique that may be used to create these micro-channels, among other methods of micro machining known to one of ordinary skill in the art. Coolant, as used in this disclosure, refers to any liquid, gel, or other flowable material that is capable of transferring heat to or from a specified device. Flowing coolant may be used to transfer heat from a device, thereby cooling it, or to a device, thereby heating it.